Quantifying threats to groundwater resources in the Republic of Maldives Part II: Recovery from tsunami marine overwash events

Marine overwash events are among the most serious short‐term threats to groundwater supply of small coral islands. During such events, seawater can inundate small islands partially or completely, causing salinization of the aquifer. A comprehensive knowledge of freshwater lens recovery is essential for water planners on these islands. In this study, a numerical modelling approach is used to quantify recovery of the freshwater lens on 4 islands of the Maldives after a tsunami‐induced overwash event similar to that experienced from the Indian Ocean earthquake in December 2004. The islands vary in size (0.2 to 10.1 km²) and span the climatic regions of the Maldives. A tested 3‐dimensional SEAWAT groundwater model for each island is used to simulate the recovery process. Recharge rates from historical rainfall data and from global climate models are imposed on each island during the post‐overwash recovery period. The effect of groundwater pumping on lens recovery also is examined. Results show abrupt decrease in fresh groundwater volumes for each island, followed by recovery that is significantly influenced by island size and recharge patterns. Overall, salinization is more widespread on small islands (<1 km²), but recovery is more rapid than for large islands. Between 50% and 90% of lens recovery occurs after 2 years for small islands (<1 km²) whereas only 35% and 55% for large islands. Imposing pumping rates required to sustain the local population lengthened the recovery time between 5% and 15%, with smaller islands having the higher percentage. However, the governing factor on recovery time is the spatial extent of land surface inundation by the overwash event, with wave height and duration of the event having a negligible impact. A strong relationship exists between required recovery time and island surface area, thereby providing a method to determine recovery time for other atoll islands not investigated in this study with similar geologic structure. Our results can be used to aid in managing water resources during the post‐overwash period.     

Predicting Future Groundwater Resources of Coral Atoll Islands

Fresh groundwater reserves on small coral islands are under continual threat of salinization and contamination because of droughts, storm‐surge overwash events, over‐extraction, island community urbanization, and sea level rise. Whereas storm‐surge overwash events can cause sudden groundwater salinization, long‐term changes in rainfall patterns and sea level elevation have the potential of rendering these islands uninhabitable in the coming decades. This study demonstrates the use of a tested freshwater lens thickness simulator to estimate the groundwater resources of a set of atoll islands in the coming decades. The method uses ranges of projected rates of annual rainfall and sea level rise (SLR) to provide a range of probable lens thickness for each island. Projected rainfall is provided by General Circulation Models that accurately replicate the historical rainfall patterns in the geographic region of the islands. Methodology is applied to 68 atoll islands in the Federated States of Micronesia. These islands have widths that range between 150 and 1000 m, and experience annual rainfall rates of between 2.8 and 4.8 m. Results indicate that under average conditions of SLR, beach slope, and rainfall, almost half of the island will experience a 20% decrease in lens thickness by the year 2050. For worst‐case scenarios (high SLR, low rainfall), average decrease in lens thickness is 55%, with almost half of the islands experiencing a decrease of greater than 75% and half of the islands having a lens thickness less than 1.0 m. Small islands (widths less than 400 m) are particularly vulnerable because of shoreline recession. Groundwater on islands in the western region is less vulnerable to SLR because of a projected increase in rainfall during the coming decades. Results indicate the vulnerability of small islands to changing climatic conditions, and can be used for water resources management and community planning. Methodology can be applied to any group of islands as a first approximation of the effect of future climate conditions on groundwater resources. Copyright © 2016 John Wiley & Sons, Ltd.     

Relative role and extent of marine and groundwater inundation on a dune‐dominated barrier island under sea‐level rise scenarios

Climate change and sea‐level rise will have severe impacts on coastal water resources around the world. However, whereas the influence of marine inundation is well documented in the literature, the impact of groundwater inundation on coastal communities is not well known. Here, core analysis, groundwater monitoring, and ground penetrating radar are utilized to assess the groundwater regime of the surficial aquifer on Bogue Banks Barrier Island (USA). Then, geospatial techniques are used to assess the relative roles and extents of groundwater and marine inundation on the dune‐dominated barrier island under sea‐level rise scenarios of 0.2, 0.5, and 1.0 m above current conditions by 2100. Additionally, the effects of rising water tables on onsite wastewater treatment systems (OWTS) are modelled using the projected sea‐level rise scenarios. The results indicate that the surficial aquifer comprising fine to medium sands responds quickly to precipitation. Water‐level measurements reveal varying thicknesses of the vadose zone (>3 to 0 m) and several groundwater mounds with radial flow patterns. Results from projected sea‐level rise scenarios suggest that owing to aquifer properties and morphology of the island, groundwater inundation may occur at the same rate as marine inundation. Furthermore, the area inundated by groundwater may be as significant as that affected by marine inundation. The results also show that the proportion of land in the study area where OWTS may be perpetually compromised by rising water tables under worst case scenarios may range from ~43 to ~54% over an 86‐year‐period. Copyright © 2014 John Wiley & Sons, Ltd.     

Assessing groundwater availability of the Maldives under future climate conditions

Groundwater resources of the Republic of the Maldives are threatened by a variety of factors including variable future rainfall patterns, continued population growth and associated pumping demands, rising sea level, and contamination from the land surface. This study assesses changes in groundwater availability due to variable rainfall patterns and sea level rise (SLR) in the coming decades, a key component of water resources management for the country. Using a suite of two‐dimensional density‐dependent groundwater flow models, time‐dependent thickness of the freshwater lens is simulated for a range of island sizes (200 to 1,100 m) during the time period of 2011 to 2050, with recharge to the freshwater lens calculated using rainfall patterns provided by general circulation models for the three distinct geographic regions of the Maldives. The effect of SLR on the freshwater lens is quantified using estimates of shoreline recession and associated decreases in island width. If rainfall is solely considered, groundwater availability is projected to increase, as lens thickness during the 2031–2050 time periods is slightly greater (1–5%) than during the 2011–2030 time period. However, including the impact of SLR indicates an overall decrease in lens thickness, with drastic decreases (60% to 100%) projected for small islands (200 m) and moderate decreases (12% to 14%) expected for 400 m islands, which accommodate one third of the national population. Similar methodologies can be used for other atoll island nations, such as the Republic of Marshall Islands, Federated States of Micronesia, and the Republic of Kiribati. For the Maldives, results from this study can be used in conjunction with population growth estimates to determine the feasibility of including groundwater in water resources planning and management for the country.     

Coastal profile response to sea level rise: a process‐based approach

Prevailing ideas and calculations of coastal response to sea level rise (SLR) are often based on the Bruun model (Bruun P., Sea‐level rise as a cause of shore erosion, Journal Waterways Harbors Division, ASCE 88 : 117–130, 1962) that predicts upward and landward transfer of an equilibrium profile during SLR through offshore sediment transport on the shoreface. The model is based on a number of assumptions of questionable validity as well as outdated concepts on how sediment is transported across the shoreface. This contribution takes a numerical modelling approach that is based on first‐order processes contributing to the movement of sediment across the shoreface. Using a wave transformation model that predicts hydrodynamic processes driving cross‐shore sediment transport and an energetics‐based model for the coupling between hydrodynamics and sediment transport, we show that cross‐shore sediment transport is mainly onshore directed at the boundary between the lower and the upper shoreface, in agreement with the model proposed by Davidson‐Arnott (Conceptual model of the effects of sea level rise on sandy coasts, Journal of Coastal Research 21 : 1166–1172, 2005). The transition from onshore to offshore directed transport is located well within the surf zone and with a rising sea level this transition point becomes displaced landward and upward. Tests also show that substrate slope is of fundamental importance to the manner in which beaches react to rising sea level. Copyright © 2012 John Wiley & Sons, Ltd.     

Apparent dynamic stability of the southeast African coast despite sea level rise

The coast of southeast Africa is dominated by sandy beaches that tend to be confined within log‐spiral or headland‐bound embayments. Investigations using serendipitous air imagery data set have been previously undertaken and conclusions drawn about the stability of the coast. We show that conclusions drawn from this data, with respect to the high water mark (HWM) position are fraught with errors, which include tidal state, pressure regime, beach slope, high‐swell erosion, seasonal and multi‐annual changes. We highlight and discuss these sources of error, together with their magnitudes. The most significant of these are the high‐swell, seasonal and multi‐annual variations. From case studies we show that the seasonal beach rotation and long‐term beach width variation are responsible for tens of metres of unaccounted HWM variation, 30 to 50 m is common, with maximums reaching 60 to 100 m. Overall the southeast African coastline appears to be in a state of long‐term dynamic equilibrium. There is no evidence of any sea‐level rise‐forced transgression in the coastal sediment budget, despite sea‐level rise (SLR). If such a signal is, in fact present, it is lost within the beach width variation. Some southeast African coastal reaches are suffering chronic erosion, but these are related to anthropogenic impacts. The extreme difficulty of placing a HWM, with any temporal validity on this coast precludes the routine use of the Bruun Rule. Although no transgressive signature is found, there is evidence of a decreasing coastal sand budget as a result of anthropogenic or natural climate change, or both. This decrease in the coastal sand volume is likely to result in increased future erosion. Copyright © 2016 John Wiley & Sons, Ltd.     

The impact of climate change on sea level rise at Peninsular Malaysia and Sabah–Sarawak

The sea level change along the Peninsular Malaysia and Sabah–Sarawak coastlines for the 21st century is investigated along the coastal areas of Peninsular Malaysia and Sabah–Sarawak because of the expected climate change during the 21st century. The spatial variation of the sea level change is estimated by assimilating the global mean sea level projections from the Atmosphere–Ocean coupled Global Climate Model/General Circulation Model (AOGCM) simulations to the satellite altimeter observations along the subject coastlines. Using the assimilated AOGCM projections, the sea level around the Peninsular Malaysia coastline is projected to rise with a mean in the range of 0.066 to 0.141 m in 2040 and 0.253 m to 0.517 m in 2100. Using the assimilated AOGCM projections, the sea level around Sabah–Sarawak coastlines is projected to rise with a mean in the range of 0.115 m to 0.291 m in 2040 and 0.432 m to 1.064 m in 2100. The highest sea level rise occurs at the northeast and northwest regions in Peninsular Malaysia and at north and east sectors of Sabah in Sabah–Sarawak coastline. Copyright © 2012 John Wiley & Sons, Ltd.     

Projected risks to groundwater‐dependent terrestrial vegetation caused by changing climate and groundwater abstraction in the Central Perth Basin,Western Australia

The effect of potential climate change on groundwater‐dependent vegetation largely depends on the nature of the climate change (drying or wetting) and the level of current ecosystem dependence on groundwater resources. In south‐western Australia, climate projections suggest a high likelihood of a warmer and drier climate. The paper examines the potential environmental impacts by 2030 at the regional scale on groundwater‐dependent terrestrial vegetation (GDTV) adapted to various watertable depths, on the basis of the combined consideration of groundwater modelling results and the framework for GDTV risk assessment. The methodology was tested for the historical period from 1984 to 2007, allowing validation of the groundwater model results' applicability to such an assessment. Climate change effects on GDTV were evaluated using nine global climate models under three greenhouse gas emission scenarios by applying the climate projections to groundwater models. It was estimated that under dry climate scenarios, GDTV is likely to be under high and severe risk over more than 20% of its current habitat area. The risk is also likely to be higher under an increase in groundwater abstraction above current volumes. The significance of climate change risk varied across the region, depending on both the intensity of the change in water regime and the sensitivity of the GDTV to such change. Greater effects were projected for terrestrial vegetation dependent on deeper groundwater (6–10 m). Copyright © 2013 John Wiley & Sons, Ltd.     

Sea‐level rise impact on fresh groundwater lenses in two‐layer small islands

The fresh groundwater lenses (FGLs) of small islands can be highly vulnerable to climate change impacts, including sea‐level rise (SLR). Many real cases of atoll or sandy islands involve two‐layer hydrogeological conceptualizations. In this paper, the influential factors that affect FGLs in two‐layer small islands subject to SLR are investigated. An analytical solution describing FGLs in circular islands, composed of two geological layers, is developed for the simplified case of steady‐state and sharp‐interface conditions. An application of the developed model is demonstrated to estimate the FGL thickness of some real‐world islands by comparison with existing FGL thickness data. Furthermore, numerical modelling is applied to extend the analysis to consider dispersion effects and to confirm comparable results for both cases. Sensitivity analyses are used to assess the importance of land‐surface inundation caused by SLR, relative to other parameters (i.e. thickness of aquifer layers, hydraulic conductivity, recharge rate and land‐surface slope) that influence the FGL. Dimensionless parameters are used to generalize the findings. The results demonstrate that land‐surface inundation has a considerable impact on a FGL influenced by SLR, as expected, although the FGL volume is more sensitive to recharge, aquifer thickness and hydraulic conductivity than SLR impacts, considering typical parameter ranges. The methodology presented in this study provides water resource managers with a rapid‐assessment tool for evaluating the likely impacts of SLR and accompanying LSI on FGLs.     

Speleothems in a north Cuban cave register sea‐level changes and Pleistocene uplift rates

A flight of marine terraces along the Cuban coast records Quaternary sea‐level highstands and a general slowly uplifting trend during the Pleistocene. U/Th dating of these limestone terraces is difficult because fossil reef corals have been affected by open system conditions. Terrace ages are thus often based on geological and geomorphological observations. In contrast, the minimum age of the terraces can be constrained by dating speleothems from coastal mixing (flank margin) caves formed during past sea‐level highstands and carving the marine limestones. Speleothems in Santa Catalina Cave have ages >360 ka and show various cycles of subaerial–subaqueous corrosion and speleothem growth. This suggests that the cave was carved during the MIS 11 sea‐level highstand or earlier. Some stalagmites grew during MIS 11 through MIS 8 and were submerged twice, once at the end of MIS 11 and then during MIS 9. Phreatic overgrowths (POS) covering the speleothems suggest anchialine conditions in the cave during MIS 5e. Their altitude at 16 m above present sea level indicates a late Pleistocene uplift rate of <0.1 mm/ka, but modelling also shows uplift to have been insignificant over a long timespan during the middle Pleistocene since the cave was carved. Our study shows that some flank margin caves in the region of Matanzas are older than commonly believed (i.e. MIS 11 rather than MIS 5). These caves not only can be preserved but are good markers of interglacial sea‐level highstands, more reliable than marine abrasion surfaces. Copyright © 2018 John Wiley & Sons, Ltd.     

川-11井水位突跳对应地震初探

蒲江川-11井始建于1982年,是四川省重要的水位观测井,位于蒲江—新津—成都—德阳隐伏断裂和大兴隐伏断裂附近,近年来,该井观测环境优良,干扰小,是一口理想的水位观测井。自1982年投入观测以来,对川西地区的地震预测发挥了较好作用,特别是2002年以来,观测到了一些有益的突跳异常,并较好地对应了300 km内的4.5级以上地震。本文对川-11井异常进行了初步分析。     

四川深井水位记录昆仑山8.1级地震

昆仑山8.1级地震在四川省地震地下水观测网中引起了大多数深井水位记录的大幅度波动，数字化水位仪LN-3和大多数浮子式机械水位仪SW40-1均记录到水震波，同一口井两种不同仪器水震波的记录结果有差异，相邻井的记录不同，同震阶变结果表明除北部受张应力外主要受压应力，地震还引起了红旗水库水体冒泡，起大旋涡，库水东西对流的现象。     

Long‐term Holocene groundwater fluctuations in a chalk catchment: evidence from Rock‐Eval pyrolysis of riparian peats

The depositional history of peat‐dominated wetlands can be used to understand palaeoclimate and palaeohydrology and also constrain the impacts of future climate change. However, in chalkland valleys, seasonal water table fluctuations and a high alkalinity have diminished key environment indicators such as pollen, and there is a need for alternative investigative techniques. The method of Rock‐Eval pyrolysis can track changes in organic matter source and degradation, potentially relating to historic changes in vegetation cover. This is the first Rock‐Eval on cores from a groundwater‐dependent riparian chalk valley wetland combined with radiocarbon dating. The dating showed that the cores represented approximately 4000 years of depositional history. Changes in hydrocarbon chemistry including normal alkane composition of the peat indicated shifts of around 500 to 1000 years between terrestrial and more aquatic species, relating to periods of climate wetness. These climatic shifts are broadly consistent with other evidence from ombrotrophic peatland and lacustrine sediments across northwest Europe. However, the connection between climate wetness and groundwater dependent chalkland wetlands is complicated by external anthropogenically driven factors relating to land use and vegetation cover changes in the catchment. Nonetheless, this study suggests that Rock‐Eval pyrolysis is a useful and cost‐effective tool that can provide evidence for long‐term Holocene groundwater fluctuations. Copyright © 2016 British Geological Survey.     

Holocene evolution of a rock‐bounded barrier‐lagoon system,Cíes Islands,northwest Iberia

Coastal geomorphology results from the combined effects of contemporary dynamics, sea‐level rise and the inherited geological framework, yet the relative importance of these driving mechanisms may change throughout the evolutionary history of coastal deposits. In this contribution, we analyse the depositional history of the Cíes Islands barrier‐lagoon system, based on lithofacies, radiocarbon ages, and pollen analysis. Our results reveal a sedimentary sequence that provides evidence for striking changes in the dynamical functioning of this complex since the mid‐Holocene. The sedimentary sequence commenced about 7700 cal years bp by fresh‐water ponding of an upland depression located about 4 m below present mean sea‐level. Fresh‐water ponds were infilled by aeolian sediments following a gradual lowering of the water‐table 4000 cal years bp . Post‐3600 cal years bp sea‐level rise allowed water oscillations to reach the elevation of the bedrock causing the inundation of fresh‐water ponds and subsequent lagoonal and marine sedimentation. Subsequently, landward and upward migration of a sand‐barrier led to overwash and deposition of sand in the newly formed lagoon. The resultant sedimentary sequence suggests that climatic conditions played an important role controlling the sedimentation regime during the entire history of the basin; changing water‐table levels during early stages of evolution and increasing storminess during more recent times. In addition, background sea‐level rise related to the Holocene transgression was a key factor in controlling the evolution of the system, yet its influence depended to an extent on the relative elevation of the bedrock topography. Copyright © 2009 John Wiley & Sons, Ltd.     

Influence of partial confinement and Holocene river formation on groundwater flow and dissolution in the Florida carbonate platform

Much of what is known about groundwater circulation and geochemical evolution in carbonate platforms is based on platforms that are fully confined or unconfined. Much less is known about groundwater flow paths and geochemical evolution in partially confined platforms, particularly those supporting surface water. In north‐central Florida, sea level rise and a transition to a wetter climate during the Holocene formed rivers in unconfined portions of the Florida carbonate platform. Focusing on data from the Santa Fe River basin, we show river formation has led to important differences in the hydrological and geochemical evolution of the Santa Fe River basin relative to fully confined or unconfined platforms. Runoff from the siliciclastic confining layer drove river incision and created topographic relief, reorienting the termination of local and regional groundwater flow paths from the coast to the rivers in unconfined portions of the platform. The most chemically evolved groundwater occurs at the end of the longest and deepest flow paths, which discharge near the center of the platform because of incision of the Santa Fe River at the edge of the confining unit. This pattern of discharge of mineralized water differs from fully confined or unconfined platforms where discharge of the most mineralized water occurs at the coast. Mineralized water flowing into the Santa Fe River is diluted by less evolved water derived from shorter, shallower flow paths that discharge to the river downstream. Formation of rivers shortens flow path lengths, thereby decreasing groundwater residence times and allowing freshwater to discharge more quickly to the oceans in the newly formed rivers than in platforms that lack rivers. Similar dynamic changes to groundwater systems should be expected to occur in the future as climate change and sea level rise develop surface water on other carbonate platforms and low lying coastal aquifer systems. Copyright © 2012 John Wiley & Sons, Ltd.     

Prediction and prevention of the impacts of sea level rise on the Yangtze River Delta and its adjacent areas

The Yangtze River Delta region is characterized by high density of population and rapidly developing economy. There are low lying coastal plain and deltaic plain in this region. Thus, the study area could be highly vulnerable to accelerated sea level rise caused by global warming. This paper deals with the scenarios of the relative sea level rise in the early half period of the 21st century in the study area. The authors suggested that relative sea level would rise 25 50 cm by the year 2050 in the study area, of which the magnitude of relative sea level rise in the Yangtze River Delta would double the perspective worldwide average. The impacts of sea level rise include: (i) exacerbation of coastline recession in several sections and vertical erosion of tidal flat, and increase in length of eroding coastline; (ii) decrease in area of tidal flat and coastal wetland due to erosion and inundation; (iii) increase in frequency and intensity of storm surge, which would threaten the coastal protection works; (iv) reduction of drainage capacity due to backwater effect in the Lixiahe lowland and the eastern lowland of Taihu Lake region, and exacerbation of flood and waterlogging disasters; and (v) increase in salt water intrusion into the Yangtze Estuary. Comprehensive evaluation of sea level rise impacts shows that the Yangtze River Delta and eastern lowland of Taihu Lake region, especially Shanghai Municipality, belong in the district in the extreme risk category and the next is the northern bank of Hangzhou Bay, the third is the abandoned Yellow River delta, and the district at low risk includes the central part of north Jiangsu coastal plain and Lixiahe lowland.     

Prograded foredunes of Western Australia's macro‐tidal coast – implications for Holocene sea‐level change and high‐energy wave impacts

The Holocene evolution of the Canning Coast of Western Australia has largely been overlooked so far mainly due to its remoteness and low population density. We report on new data from a sequence of foredunes inside the macro‐tidal Admiral Bay, 110 km southwest of Broome. Based on sediment cores, differential global positioning system (dGPS)‐based elevation transects, and stratigraphical analyses on outcrops of the relict foredunes, we aim at reconstructing Holocene coastal changes and relative sea levels (RSLs), as well as identifying and dating imprints of extreme‐wave events. Sedimentary analyses comprise the documentation of bedding structures, foraminiferal content and macrofaunal remains, grain size distribution, and organic matter. The chronological framework is based on 26 carbon‐14 accelerator mass spectrometry (¹⁴C‐AMS) datings. Marine flooding of the pre‐Holocene surface landward of the 2.5 km‐wide foredune barriers occurred 7400–7200 cal bp , when mangroves colonized the area. After only 200–400 years, a high‐energy inter‐tidal environment established and prevailed until c. 4000 cal bp , before turning into the present supralittoral mudflat. During that time, coastal regression led to beach progradation and the formation of aligned foredunes. Drivers of progradation were a stable RSL or gradual RSL fall after the mid‐Holocene and a positive sand budget. The foredunes overlie upper beach deposits located up to >2 m above the present upper beach level and provide evidence for a higher mid‐Holocene RSL. Discontinuous layers of coarse shells and sand are intercalated in the foredunes, indicating massive coastal flooding events. One such layer was traced over three dune ridges and dated to c. 1700–1550 cal bp . However, it seems that most tropical cyclones induce net erosion rather than deposition at aligned foredunes and thus, they are only suitable for reconstructing temporal variability if erosional features or sedimentation reliably tied to these events can be identified and dated accurately. Copyright © 2014 John Wiley & Sons, Ltd.     

The impact of climate change on groundwater recharge and runoff in a humid,equatorial catchment: sensitivity of projections to rainfall intensity

Abstract

Projected warming in equatorial Africa, accompanied by greater evaporation and more frequent heavy precipitation events, may have substantial but uncertain impacts on terrestrial hydrology. Quantitative analyses of climate change impacts on catchment hydrology require high-resolution (<50 km) climate data provided by regional climate models (RCMs). We apply validated precipitation and temperature data from the RCM PRECIS (Providing Regional Climates for Impact Studies) to a semi-distributed soil moisture balance model (SMBM) in order to quantify the impacts of climate change on groundwater recharge and runoff in a medium-sized catchment (2098 km²) in the humid tropics of southwestern Uganda. The SMBM explicitly accounts for changes in soil moisture, and partitions effective precipitation into groundwater recharge and runoff. Under the A2 emissions scenario (2070–2100), climate projections from PRECIS feature not only rises in catchment precipitation and modelled potential evapotranspiration by 14% and 53%, respectively, but also increases in rainfall intensity. We show that the common application of the historical rainfall distribution using delta factors to the SMBM grossly underestimates groundwater recharge (i.e. 55% decrease relative to the baseline period of 1961–1990). By transforming the rainfall distribution to account for changes in rainfall intensity, we project increases in recharge and runoff of 53% and 137%, respectively, relative to the baseline period.     

Holocene salinity fluctuations of the East Korean lagoon related to sea level and precipitation changes

Detailed diatom records within core sediments from Maeho Lagoon along the Eastern coast of South Korea revealed that the ecological dynamics of the lagoon during the Holocene were associated with relative sea level and regional precipitation. Accelerator mass spectrometry (AMS) ¹⁴C dating indicates that sediment accumulation began prior to 8300 cal. year BP, and that the lagoon formed around 8000 cal. year BP. The salinity level of the lagoon increased until 5000 cal. year BP, and then decreased. Long‐term trends in salinity were dependent upon changes in sea level: periods of high salinity in the lagoon were generally coincident with periods of high sea levels along the east coasts of Korea and Japan. On the other hand, multicentennial‐scale fluctuations in diatom assemblages and magnetic susceptibility (MS) suggest that a 400 year fluctuation in salinity was regulated by changes in precipitation in the area of this lagoon. Changes in the westerly jet stream, controlled by variation in solar irradiance, had an important influence on precipitation volume in South Korea, suggesting that the patterns of the westerly jet stream fluctuate on a 400 year cycle.     

Morphology of the Itapeva to Tramandai transgressive dunefield barrier system and mid‐ to late Holocene sea level change

The surface morphology of the transgressive dunefield barrier extending from Itapeva to Tramandai along the northern littoral of Rio Grande do Sul, is examined and an attempt is presented to link morphological changes across the barrier to Holocene sea level changes. The 4·5 km wide Holocene barrier displays two typical morphologies: an inner part dominated by large‐scale, continuous alongshore, overlapping dunefield phases comprising sand sheets, dunes, deflation plains and precipitation ridges; and an outer part dominated by discontinuous, medium‐ to small‐scale, triangular to lobate transgressive dunefield phases, cut by both active and relict (palaeo‐) creeks or washouts. Holocene sea level in the region rose to c. +1 to +3 m above present reaching a maximum around 5100 years bp and then progressively fell to the present level. We argue that the effect on barrier development was to suppress the development of a drainage system during the rising and maximum stages, and encourage the development of an organized drainage system in the form of regularly spaced washouts during the falling period, and that this change in sea level from rising to falling therefore produced the large‐scale differences in barrier morphology. Copyright © 2006 John Wiley & Sons, Ltd.